This invention is related to dial calipers comprising a slider slideably mounted on a caliper beam having a scale along the beam, and a dial indicator for measuring relatively small increments of the beam scale, and including a second scale along the depth rod with an adjustable pointer on the beam to permit the user to reset the zero value of the caliper when an accessory is being used on the workpiece-measuring jaws, to compensate for the distance added by the accessory to that of the workpiece.
A conventional dial caliper has a pair of jaws that engage a workpiece to either measure an outside or inside dimension. A slider carries one jaw, and the beam carries the other jaw. The two jaws are set to a base zero figure when the jaws are in abutment. When the jaws are opened to receive a workpiece, the user reads the distance between the jaws according to a scale mounted along the edge of the beam and a dial indicator mounted on the slider.
A problem arises when certain types of accessories are mounted on the jaws such as, for example, a pair of arms for measuring the inside of a cylindrical cavity in a location too deep for the conventional jaws. The problem is that the arms occupy a certain amount of space between the jaws and thus increase the reading along the scale over the actual dimension of the workpiece. Usually lengthy and cumbersome calculations must be made to first find the actual deviation added or reduced to the zero reading on the scale on the beam, and then the user must add or subtract that deviation from the measurement indicated.